The present invention relates to a diversity antenna apparatus usable with various communication devices to enable transmission and/or reception of a signal having a polarized waveform.
Communication devices, such as a portable telephone set and other portable-type devices, may utilize a diversity antenna apparatus having a plurality of antennae which are selectively used to assure a high anti-multi-path characteristic or multi-path resisting property. An example of such portable communication device is illustrated in FIG. 1. As shown therein, portable communication apparatus 100 includes two antennae 101 and 102 which are spaced apart from each other by a distance equal to or greater than xcex/4 where xcex is the wavelength of an electromagnetic wave which may be transmitted and/or received by the antennae 101 and 102. The portable communication apparatus 100 transmits and/or receives a signal using the one of antennae 101 and 102 which provides a more favorable condition.
The portable communication apparatus 100 may use a circuit such as that illustrate in FIG. 2 to select one of the two antennae. As shown in FIG. 2, the antennae 101 and 102 are respectively connected to receivers 103 and 104. Outputs of the receivers 103 and 104 are supplied to a reception level comparator 105 and compared thereat to each other so as to determine the one of the antennae 101 and 102 which exhibits a more favorable output characteristic and form a comparison signal therefrom. Such comparison signal is supplied from the reception level comparator 105 to an antenna changeover switch 106 which, in response thereto, switchably selects the appropriate output signal from the receiver 103 or 104 which corresponds to the antennae 101 or 102 which exhibits a more favorable output characteristic.
In the portable communication apparatus 100, to assure an acceptable transmission and/or reception state the two antennae 101 and 102 are disposed from each other by a predetermined distance (such as a distance equal to or greater than xcex/4) so as to make use of a so-called space divesity effect. In other words, the antennae are spaced sufficiently apart from each other such that the manner in which each antenna undergoes fading varies independently of each other. An acceptable transmission and/or reception state may be provided unless the fading associated with both of the two antennae 101 and 102 fall is significant.
FIG. 3 illustrates a portable communication apparatus 110 which utilizes a diversity antenna apparatus. As shown therein, the portable communication apparatus 110 includes two antennae 111 and 112 disposed on different faces thereof. The portable communication apparatus 110 transmits and/or receives a signal using the one of antennae 111 and 112 which exhibits a more favorable state. Such antenna may be selected in a manner similar to that of portable communication apparatus 100.
In the portable communication apparatus 110, the antenna 112 is set to have a sharp directivity so as to assure a high gain thereby allowing an electromagnetic wave used for transmission and/or reception to reach over a relatively large distance and assure a good anti-multi-path characteristic. Since the portable communication apparatus 110 transmits and/or receives a signal using the one of the antennae 111 and 112 which exhibits a more favorable state, a good transmission and/or reception state can be assured using a radiation pattern diversity effect.
Radio communication between various apparatus in a home, office or the like may occur. In such radio communication, it may be necessary to transmit and receive a signal between floors in a building. Further, a communication apparatus (such as a portable-type communication apparatus) may be inclined at any angle with respect to the ground while being used. In this situation, if an antenna is fixed to the body of the portable communication apparatus, then the orientation of the antenna may vary in response to the inclination of the apparatus body.
The diversity antenna apparatus described above are for outdoor use or for use on the same floor in a building. These apparatus may have a radiation pattern associated therewith which provides a favorable gain in a direction parallel to the ground. As an example, each antenna of the portable communication apparatus 100 and 110 may have a radiation pattern as shown in FIG. 4 or 5. That is, antennae 101, 102 and 111 may have a radiation pattern such as shown in FIGS. 4A and 4B, and antenna 112 may have a radiation pattern such as shown in FIGS. 5A and SB.
As may be apparent from FIGS. 4 and 5, it may be difficult for the above-described diversity antenna apparatus to transmit and/or receive an electromagnetic wave along a z-axis direction, that is, in an upward or downward direction. Therefore, although such diversity antenna apparatus may favorably resist against multi-path interference in the same plane, such apparatus may not be suitable for transmission and/or reception in all three principal dimensional directions. In addition, since such diversity antenna apparatus may be used with a linearly polarized wave (such as a horizontally polarized wave or a vertically polarized wave), the transmission and/or reception condition may vary greatly due to the angle of the antenna with respect to the ground.
Accordingly, the above-described diversity antenna apparatus may not be able to ensure acceptable or stable transmission and/or reception conditions when used for radio communication in a home, office or the like or applied to various portable communication apparatus because the polarization plane of the signal varies depending upon the location and/or orientation of the communication apparatus.
According to the present invention, a diversity antenna apparatus is provided which comprises (a) a plurality of antennae for transmitting and/or receiving a circularly polarized wave, and b) an antenna selection circuit which selects one of the antennae for transmission and/or reception based on information representative of reception levels of the antennae, in which a first group of the antennae provides a first substantially semispherical radiation pattern and a second group of the antennae provides a second substantially semispherical radiation pattern such that the first and second groups of antennae as a whole provide a substantially spherical radiation pattern.
By utilizing a diversity antenna apparatus having a plurality of antennae with a substantially spherical radiation pattern associated therewith, an acceptable transmission and/or reception state may be provided in all directions. As such, the transmission and/or reception state may not be significantly varied due to an angular change of the antennae with respect to the ground. Further, a circularly polarized wave may be used for transmission and/or reception. As a result, an augmented antimulti-path characteristic can be achieved. Therefore, such diversity antenna apparatus may be suitably adapted for use in a home, office or the like or for use with various portable communication apparatus.
The above and other objects, features and advantages according to the present invention will be apparent from the following detailed description of the illustrated embodiments when read in conjunction with the accompanying drawings in which corresponding components are identified by the same reference numerals.